Resolved. Of course I did it to myself, but #Xcode could have warned me. Package dependencies either direct or indirect in my project are A <- B <- C <- D <- E <- App where x <- y means x is a dependency of y. I was writing tests for package C. To make test setup easier I called functions in package D and E, adding D and E as dependencies to C. Oops. Don't do that. Apparently adding C and C_C is how Xcode handles circular dependencies.